An Interview with EUGENE P. WIGNER OH 130 Conducted by William Aspray on 12 May 1987 Princeton, NJ Charles Babbage Institute The Center for the History of Information Processing University of Minnesota, Minneapolis Copyright, Charles Babbage Institute 1 Eugene P. Wigner Interview 12 May 1987 Abstract Wigner talks about his association with John von Neumann during their school years in Hungary. He discusses their graduate studies in Berlin and their appointments to Princeton in 1930. Wigner discusses von Neumann's contributions to the theory of quantum mechanics, Wigner's own work in this area, and von Neumann's interest in the application of theory to the atomic bomb project. 2 EUGENE P. WIGNER INTERVIEW DATE: 12 May 1987 INTERVIEWER: William Aspray LOCATION: Princeton, NJ ASPRAY: This is an interview on the 12th of May, 1987 with Dr. Eugene Wigner in his office at Princeton University. Could I ask you first to talk about John von Neumann's early school education and whether there was any demonstration of mathematical promise at that age? WIGNER: Yes, he did have a great promise of that. He went to the Lutheran High School in... ASPRAY: ... in Budapest. I've been there, by the way, to visit. WIGNER: Is that so? ASPRAY: Yes. WIGNER: Yes. No, it isn't a high school. ASPRAY: No. WIGNER: Yes. And that... Our mathematics teacher, Lazll Racz (?) noticed what gifts he had as a mathematician. And he gave him private classes -- a great many -- about three times a week. He refused any compensation for it even though Johnny's parents were quite wealthy. But he felt he did it for himself, and he was a wonderful teacher. ASPRAY: What did he teach him in these private...? WIGNER: Mathematics. Well, I think it probably started with mathematical geometry. 3 ASPRAY: Yes. WIGNER: And that was very nice; and he learned well and was delighted. He remained very friendly towards his colleagues and even to me who was one year ahead of him in class, but about two and a half years behind him in mathematics. ASPRAY: I see. This went on at what ages of his life? WIGNER: It started, I think, when he was thirteen and ended, of course, when he was 18 when he graduated from high school. ASPRAY: Was he also taking classes at the University while he was still in high school, or studying with the professors? WIGNER: I don't think so, but I can't be absolutely sure. But he was very much taken care of by this Moratt (?) and other teachers who thought very highly of him and even liked him. ASPRAY: I take it from the fact that you were at so many places together that you had a long and lasting friendship. So you knew him well in this early period also; is that right? WIGNER: Not as well as my own classmates. We met sometimes. We took walks together. He liked to walk and explain things and teach me a little mathematics, a little history perhaps. And it was very nice. But these were walks. And I took many more walks with other friends who also were interested in conversations. ASPRAY: Now, you both ended up in Zurich studying not long after that. Is that right? 4 WIGNER: I did not study in Zurich. ASPRAY: Oh, you didn't study in Zurich; he did, though. WIGNER: He did, yes. ASPRAY: That's right. So the two of you were apart for some period of time. WIGNER: Well, yes, we were apart for a period of time. Eventually, he came also to Berlin in Germany. And we studied there. And we often attended the same colloquium, although he rarely came to the physics colloquium. ASPRAY: I see. So he only came occasionally, whereas you were there on a regular basis; is that right? WIGNER: I tried to be there on a regular basis. ASPRAY: He was there as a private docent? WIGNER: Not in the beginning, of course. I think everybody has to study at least four years. And, of course, I was a little ahead of him, because I am a year older than he was. But we met occasionally. He liked to go to conferences, and celebrations. We met rather frequently. ASPRAY: In Berlin, who were the scientific influences on him? Who did he take courses with, or talk to, or...? WIGNER: He took courses with mathematics. And there was a very excellent, famous mathematician there. Do you know his name? He gave good classes and very interesting, and he was interested, and his classes were interesting; and Johnny enjoyed that. He studied at the University. I studied at the Institute of Technology. So we didn't meet that way. But the colloquium to which I went was at the University; and I sneaked away from the Institute of 5 Technology for those. ASPRAY: I see. You said that von Neumann did come sometimes to the physics colloquium, though. WIGNER: Yes, sometimes. ASPRAY: What were his interests in physics at this time? WIGNER: Well, you know there was a great deal of difficulty in theoretical physics. The quantum theory was not self consistent. It became self consistent much later. And it's not consistent with the general, or even the special relativity of theory even now. And at that time it was not really consistent with itself. ASPRAY: Yes, I understand... I know about that. Did he know about the problems in quantum mechanics before he came to Berlin, or did he learn about it there? WIGNER: I think he learned about it there, but I could not swear to it. I knew some of the problems. It was very evident that you don't know how to quantize things. And of course it was changed with a terrible revolution which postulates that the positions and velocities of the particles are not at one time definite. And, altogether, that the old classical mechanics does not apply to very small, light particles. ASPRAY: Yes. WIGNER: You know about that. ASPRAY: Yes, I know about that. Could you describe to me how von Neumann got involved in his work in foundations of quantum mechanics, and what you see as being his contribution? 6 WIGNER: Well, you know those things are not so very clear. He formulated quantum mechanics when quantum mechanics, not quantum theory, was created, particularly by Schroedinger. It was evident that the old-fashioned scripture, of the state of the system is not varied. And Johnny worked on the question, "What happens if you make observations?" And his theory of observations, although it is not much advertised, and although it is not solely due to him it has a great deal of influence even in present day quantum mechanics instruction. I remember he postulated that every self-adjoined operator can be observed. And that was wonderful, and explained why you can't observe position and velocity, can't produce a state with a definite position and velocity, and so on. I remember that very much later (I think in 1933) I proved that not all self-adjoined operators can be observed. Only very few can be, yes -- and should be. I proved that the others can't be. And you know, I was a little worried about it, because I thought he would object to it. And the strange thing is that my article, which became quite well known later on was not accepted by the first journal to which I submitted. And I told this to Johnny and he said, "Yes, that's a very interesting theorem. Give it to us. We'll publish it in the Annals of Mathematics." And that impressed me very much. He realized that his theory had limitations. And he accepted that and was not angry at the proof. No, he was a very reasonable person in that way. ASPRAY: Yes. What did the other people that were working in the quantum theory at that time, the big names, think of von Neumann's contribution? WIGNER: Well, you know, I think they realized that this is very interesting mathematically... but I don't think they accepted it fully, and they didn't feel that's very relevant, and so on -- so that it was more disregarded than reasonable. And I think eventually it was slowly realized that it is a very important thing to formulate quantum mechanics definitely from ground up -- from basic principles up, and that we'll do a great deal of help. And in that way it did have eventually a great deal of influence. But originally it was said, "Yes, it's very interesting but I don't want to do it right now," was the general reaction. ASPRAY: I see. I guess that von Neumann was seen by the physicists, really, as a mathematician rather than as a physicist. Is that correct? 7 WIGNER: I think so, yes. That was a mathematical theory -- the theory of self adjoined operators have characteristic values and characteristic vectors and so on. ASPRAY: How would you evaluate von Neumann as a physicist. I mean, we always think of him as a mathematician, but he obviously knew some physics. WIGNER: Oh, he knew a great deal of physics. I don't think his contributions were to basic physics (except for this one, which turned out to have been very important). I don't know of any other very basic contribution of his. He was not so much interested in small phenomena and special theories. It was very different in his contribution to nuclear weapons.